1. Field of the Invention
This invention relates to a current overload protection circuit which will interrupt current flow from a power source to a load operable with both AC and DC power sources.
2. Background of the Invention
The problem of current overload protection is typically solved by the use of fuses or circuit breakers which suffer from the disadvantage in some applications in that they cannot be automatically reset. Resettable fuses are available, but such fuses usually employ temperature coefficient resistors which increase their resistance with current increases. Such resettable fuses do not provide precise repeatable performance.
When the power source is limited to a DC power source, current overload protection has been achieved by means of a series pass transistor. However, to use this solution for an AC power source, all of the circuitry of the protection circuit must be duplicated. A relay operated in response to current detection circuitry has been used in some applications. However, relays require a lot of circuit board real estate. Solid-state relay circuits for current overload protection suffer from the disadvantage of being susceptible to operation in a linear region between full on and full off causing excessive heating and power dissipation. In addition, they require excessive packaging volume when several isolated loads have to be protected due to the requirement for a dedicated power supply for each protection circuit to maintain isolation.
The present invention improves on prior art solutions by requiring a minimum number of components, all of which are readily available, to protect both AC and DC high voltage loads and the system is readily expandable to protect multiple, isolated loads without requiring isolated power sources for individual protection circuits protecting different isolated loads.